Ben Krasnow 3D prints a clear Einstein-Szilard refrigerator powered by flame

Thermodynamics visible through clear resin

Absorption refrigerators have long held a practical role in industrial facilities and camper vans because they run entirely on heat and contain no moving parts. Traditional models rely on ammonia and water mixtures that require higher operating pressures than typical plastic or glass chambers can withstand, as reported by Hackaday. To reveal the internal fluid motion, Krasnow turned to the alternative patent design formulated by Albert Einstein and fellow inventor Leó Szilárd.

The system was manufactured using 3D printing in clear resin, enabling direct observation of the boiling, evaporation, and condensation steps. A solid copper block transfers heat from an open flame directly into the boiler chamber. While ammonia solutions gradually dissolve copper over time, Krasnow found the arrangement fully functional for experimental demonstration.

Swapping butane for safer perfluoropentane

The Einstein-Szilard cycle introduces a third fluid into the process to avoid extreme pressure thresholds. In this setup, heat separates a concentrated ammonia-water solution by boiling off ammonia gas, which then reduces the partial pressure over a liquid refrigerant and forces it to evaporate. Both vapors enter a chamber where water dissolves the ammonia, leaving the refrigerant vapor to condense and repeat the closed loop while the liquid solution returns to the boiler.

While the original design typically uses butane as the volatile refrigerant, Krasnow substituted perfluoropentane to eliminate explosion hazards alongside an open flame. The nonflammable chemical allowed the pressurized resin apparatus to run safely under direct thermal heating.

Airlocks and real temperature drops

Operating the clear prototype revealed specific fluid-dynamic hurdles. Because the closed system maintains nearly uniform pressure throughout its loop, even a tiny vapor bubble trapped in the wrong channel can create an airlock and stall fluid circulation.

Despite the narrow margins, Krasnow adjusted the flow and achieved a drop of 5 degrees Celsius below the ambient temperature, demonstrating a unique thermal innovation. Krasnow also pointed out an unusual thermodynamic application: with high-proof alcohol, burning a fraction of the liquid generates enough heat to chill the rest of the drink.

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